Telephonic transmitter.



P. STRAGIOTTI. TELEPHONIG TRANSMITTER. APPLiGATION FILED AUG.11, 1908.

. Patented May 17, 1910.

wi 7x209}; gamma I EIE'JEl RXO STRAGIOTII, F HURLEY, WISCONSIN.

TELEPHONIC TRANSMITTER.

Specification of 'Lette rs Patent. Patented May 17, 1910.

Application filed August 11, 1908. Serial No. 448,025.

To all whom it may concern:

Be it known that I, PIETRO STRAoIo'r'rI, a subject of the King of Italy, residing at Hurley, in the .county of Iron and State of \Visconsin, have invented certain new and useful Improvements in Telephonic Transmitters; and I'do declare the following to be a full, clear, and exact description of the invention,such as will enable others skilled in the art to which it appertains to make and usethe same, reference being had to the accompanying drawings, and to the letters and figures of reference marked thereon, which formla part of this specification.

My invention relates to the class of telephony, but more particularly to a difl'erential telephonic transmitter and the specific electric wiring therefor; and my invention consistsin the application of an autoinduction coil to the differential micro-phone in such manner as torender the micro-phone more eflicient and sensitive.

A further object of my invention consists in providing a system in which the constant current necessary to act may be sent from the central to the telephonic line during the time of the communication, and which is at the same time used for a signal in the central.

In other words my invention further consists in providin battery circuit ceding the microphone, which is usually in the subscribers box, is in this system made longer, extending from the central to the subscribers box.

A further object of my inventionis to provide a system in which the effective telephonic line resides in the secondary of the transformers which may pass through a condenser, this secondary being a derived circuit of the telephonic box.

My invention also consists in certain other novel details of construction and in combinations of parts, all of which will be first fully described and afterward'specifically pointed out in the appended claims.

Referring to the drawings: Figures 1, 2 and 3 illustrate the systems of wirlng. Fig. 4 is. a-viewof the differential microphone. Fig. 5 illustrates a modification showing a form of impedance obtained from two identical .coils inserted in the two derived circuits.

a system in which the equal transformers. The current produced by the battery passes through the inductive reactance, goes to the central electrode of the micro-phone Where it forks, each branch passing through the primary of a transformer. The primaries are thereby in derived circuits, while the secondaries, (being connected to the same conductor E and E) are in series, so that to any inductive action of the same direction in the two primaries,

induction forces of the opposite direction correspond 1n the secondary from which no induction current corresponds to any equal increasing or diminishing of the current in the two primaries; but when under the influence of the micro-phone the comparative value of the-two primary currents changes to the increasing of the one and to the equal contemporary diminishing of the other (which must happen if the inductive reactance I be of sufficient efliciency) then there are induction forces in the secondary which sum together, and a current results. in this, proportioned to the variation of the difference which is forming between the two principal currents. By the use of two distinct transformers where the primary currents always flow in the same direction the iron is always magnetized in the samed-i-rection and the magnetic permeability is nearly constant allowing a very correct transmission of the wave to the secondary. I The voice vibrations produce a differential variation of resistance in the two arts of the micro-phone, so that if the idea circuit is considered, which asses through the two parts of the micro-p one and the two primaries of the transformers (where the ohmic resistance is almost wholl in the micro-phones) it is found that under the effect of the vibrations of the central electrode the greatest part of this resistance is oscillating from the right to the left and vice versa of the two symmetrical ,parts MP'Q and MP Q, synchronically with the sound vibrations, and therefore the greatest part of the current, under oes analogous oscillations in op osite directions. The said oscillations prod nce currents in the secondary (telephonic) circuit} which are much more energetic than the usual ones, because in this instance the difference of electric tension through the carbon does not change, whence the sparking is diminished, and therefore the current through each m1- cro-phone may be increased. Inv this invensystem of telephony is possible.-

. In the differential micro-phone the total constant current forks in two branches alike in every respect, either corresponding to that portion in the usual micro-phone circuits which comprises a micro-phone and the primary induction coil. So far there is no difference, but in every part of the circuit connected to the micro-phone, the battery included, there flows one and the same current, and therefore to any action of the microephone to which a variation of current is to correspond, every part of the circuit counter-acts so as to oppose such variation 5 while with the differential micro-phone outside of the two branches referred to there flows constant current and ,nowhere can there arise any such counter-action. It is to be observed that in the carbon microphone the only limit in the amount of current is established by the sparking. In the differential micro-phone it cannot be said that no sparking occurs as some reaction cannot'be avoided, but it can be relied on that the fact that the reaction above explained does not exist. Conse uentl with the same amount of current t roug each microhone, as with usual micro-phones, no suc amount of sparking will be produced. Theaction of the micro-phone, therefore, becomes more efficient, because the battery resistance and those extraneous to the micro-phone are of no consequence, and certainty of the. action is increased because the action of the two parts of the differential micro-phone is opposite so that not even the faintest sounds of the voice will be lost. This diflerential micro-phonic apparatus assisted by an inductive reactance allows a peculiar application to telephony by which the centra telephonic service is a owed a convenient disposition which obviates some disadvantages usually existing.

Referring now to Fig! 2 which is a diagram of my new system; A represents the subscriber and G the central, A and C being connected by the line, with two wires or with only one wire and the ground. There is a battery of cells or of accumulators B in C which at the same time may serve several subscribers.

From the two points mw outside of the battery, the line, especially to each sub-- is opened when there is no telephonic communication, but is intended to introduce the service connections. In Q'there is the calling button which allows the alternating current from the generator'to pass in the line to go to the bell. The line starts from OO, and the box of the subscriber has in ee.the connections with the line. lVhen the receiver ris hung to the hook it the line is closed through debt, which includes a condenser c and the bell Z). The constant current of the battery Bof the central cannot pass because of the condenser 0; while by means of the calling button Q an alternating current will pass to make the bell act. When the receiver "'r is taken off the hook it the circuit through the bell is broken and the two other circuits are introduced; one throu h the receiver, the secondaries of the transformers and the condenser C (instead of which the line D (Fig. 3) may be substituted) to II, the connecting point with the other circuit. This other circuit passes through the induction reactance I and goes to the central electrode of the micro-phone M where it forks and goes through each of the other electrodes and through each of the primaries I of the transformers and thence to the connecting point 111'. By introducing these two circuits constant current passes in the line, and therefore the lamp is lighted, which shows the central that the subscriber calls. The whole continuous current passes through the micro-phone M if there is the condenser C: but when there might be a particular ohmic resistance in the circuit through the receiver and the secondaries of the transformers, the apparatus will act equally well, allowing constant feeble current to pass in this circuit. If this current is a little stronger than the greatest intensity of the telephonic currents it will be suiticient to p'olari ze the receiver which will not need a permanent magnet. When from the central any other subscriber is called and communication with this one is established through the spring-j ack S the two subscribers will. be in the same condition as to the central, and the telephonic currents-originated in the secondaries of the transformers cannot pass-in the microphonic circuit III IM-III northrough the battery B in the-central circuit, because of the very strong reactances, so that the said current will run almost wholly in the'analogous circuit of the subscribers receiver. When the telephonic communication is over and the subscribers hang their receivers on the hooks terru ted, because through the spring-jack S ony the wiresof analogous polarity are connected 1n order to avoid short circuitlng,

the current coming from the battery is inand'the lamp goes out which indicatcsto the central that the connection must be reactance, which is anauto induction coil. of so strong auto induction that the continuous current passing through cannot undergo any sensible variation.

The principal feature of this application istheuse of an auto-induction coil in series with the differential microphone which on this account becomes more efiicient as will now appear. The changes of. resistance which originate in the two branches of the microphone aswell as the induction in the 15 two transformers never 1; compensate each other. The balance-acts asto make the main current oscillate while it is intended to remain constant; or in other words, together with the constant current a new oscillatory current flows. If this current divides in the two branches of the microphone into twoequal parts no current is originated in the secondaries of the transformers; but as the two branches are never in exactly the.

same condition this current does not divide into two equal parts, consequently a trou bling current is originated in the secondaries together with the telephonic current. The advantages of the auto induction coil consequently becomes apparent, for by it the current flowing, to the central electrode of the microphone is maintained exactly constant thus obviatin all troubles. However the combination 0 an auto-induction coil with a difi'erential microphone is more far reaching than in the simple improvement of this important kind. of micro hone,,for the reason that this combination 0 ers a simple and practical system of common battery tele hone as has previously been explained.

0 describe more in detail its operation, let us consider the circuit through the sec-' ondaries and the receiver which is connected at II and III -with the line conductors. Therefore at II and III this circuit forks in two derived circuits; one through the microphone and the primaries of the transformers and .the other through the line to the central, consequently the talking current generated in the secondaries divides into two parts inversely pro ortionate to the respective resistances. I the microphone had not been joined with an auto-induction coil the resistance of this. derived circuit would be relatively very small as compared with the 'line andtherefore a very small fraction of the telephonic current would flow throu h the line, but-with the auto-induction coilt 18' microphonic' circuit becomes insensible to the telephoniccurrent, and so 'noother path is offered to this current but the line to the central. In the same manner, whenthis talking current reaches 3 y at the central two-derived circuits are again formed, one

6 5 through the spring-j ack to the subscriber to be connected, and the other through the battery,

but this latter is rendered insensible by the auto-induction coil I.

If the telephonic current is considered which flows through the spring-jack from the other subscriber to be connected, this cur- 'rent flows along the line to the points II "and IIIof the subscribers box A to go practically in its entirety through the receiver as no other derived circuits are oifered to this current because of the auto-induction coils that render insensible the circuit through the battery and the circuit through the microphone. The result is that the actual telephonic circuit, that is, the circuit throu h which a telephonic current may flow esta lishes by the line the circuit through the receivers in two subscribers boxes and their connections through the spring-jacks at the central.

Referring to Fig. 5 it will be seen that I illustrate a form of impedance obtainedfrom two identical coils inserted in the two derived circuits, but this form does not diifer substantially from the impedance coil of Figs. 1 and 2, as not only this arrangement can be substituted for that but from the latter construction it is easy to obtain this form by establishing connections in Q, Q, for an impedance is then made-of one coil with double wire.

Having thus fully described the several .parts of my invention what I claim as new and desire to secure by Letters Patent ofthe United States, is;

1. The combination with a telephonic line of a bridge-circuit comprising a difierentia m clzro-phone inseries with an impedance CO1 2. The combination with a telephonic line, of a bridge-circuit com rising an impedance coil in series with a di erential micro-phone where said bridge-circuit forks in two 'derived circuits.

3. The combination. with a telephonic line, of a bridge circuit com rising a differential micro-phone wheresai bridge-circuit forks in two derived circuits, each passing through one of two identical coils wound on the same core and acting together asto' produce an impedance on the total current that flows lel circuit forks in two derived circuits passing through the primaries; of said transformers.

5. The combination with a tele honic line, of two. local parallel circuits 0? relatively hi h ohmic resistance pa-ssin throu h a recelver "1d the secondaries o ,trans ormers,

and the secondthrough an impedance coil and a differential microphone where said second parallel circuit forks in two derived .circuits passing through the primaries of said transformers.

6. The combination with a telephonic line, of three parallel local circuits, the first through a receiver the secondaries of-transformers and a condenser; the second through an-impedance coil and a difi'erential microphone where said second parallel circuit forks 1n two derived circuits passing through the primaries of said transformers; the third through a condenser and a polarized bell, and means by which said third circuit is connected to said telephonic line.

7 The combination with a telephonic line,

of three parallel local circuits, the first through a receiver the secondaries of transformers and a condenser, the second through an impedance coil and a differential microphone where said secondary-parallel circuit orks in two derived circuitspassing through the primaries of said transformers, the third through a condenser and a polarized bell, and means by which said first and second circuits are connected to said line.

In testimony whereof, I aflix my signature, in presence of two witnesses.

\ PIETRO .STRAGIOTTI.

Witnesses:

C. M. FoRREsT, C. HUGH DUFFY. 

